Osteogenic proteins are well known and described in the art. See, for example, U.S. Pat. Nos. 4,968,590; 5,011,691; 5,018,753 and 5,266,683, as well as various scholarly articles published in the scientific literature. See, for example, Ozkaynak et al. (1990) EMBO J 9:2085-2093; Ozkaynak et al. (1992), J.Biol. Chem. 267:13198-13205; Sampath et al. (1993) PNAS 90: 6004-6008; Wozney et al. (1988) Science 242: 1528-1534; Wang et al. (1988) PNAS 85:9484-9488; Wang et al. (1990) PNAS 87:2220-2224, and Celeste, et al. (1990) PNAS 87:9843-9847. The art has described how to isolate osteogenic proteins from bone and how to identify genes encoding these protein and express them using recombinant DNA technology.
The proteins that define the class of true osteogenic proteins constitute a group of proteins sharing a number of conserved structural characteristics. Each protein, on its own, can induce endochondral bone formation in a mammal when properly folded, dimerized and disulfide bonded to produce a dimeric species having the appropriate three dimensional conformation, and without requiring the addition of other osteogenic or non-osteogenic proteins. Typically, osteogenic proteins are provided to a site for bone induction in a mammal in association with a suitable matrix having the appropriate conformation to allow the infiltration, proliferation and differentiation of migrating progenitor cells. The construct of osteogenic protein adsorbed to the surfaces of a suitable matrix is generally referred to in the art as an osteogenic device. The proteins can be isolated from bone or, preferably, the gene encoding the protein is produced recombinantly in a suitable host cell. Methods for the production of osteogenic proteins and formulations of osteogenic devices are described in detail in the art. See, for example, U.S. Pat. Nos. 5,011,691, or 5,266,683, the disclosures of which are incorporated hereinabove by reference.
Improved methods for the recombinant expression of osteogenic proteins is an ongoing effort in the art. It is an object of this invention to provide an improvement in the methods for producing and purifying osteogenic proteins having high specific activity, and for formulating osteogenic devices comprising these proteins. Still another object is to provide means for distinguishing between the soluble form of the protein and the mature osteogenic protein species typically utilized in formulating osteogenic devices, and to provide polyclonal and monoclonal antibodies capable of distinguishing between these various species. Another object is to provide methods for producing antibodies which can recognize both forms of the protein. Still another object is to provide methods for monitoring each and all these forms of the protein in a fluid, including serum and production media. U.S. Pat. No. 4,857,956 and Urist et al. (1984) Proc. Exp. Bio. Med. 176: 472-475, describe a serum assay for detecting a protein purported to have osteogenic activity. The protein is not a member of the family of osteogenic proteins described herein, differing in molecular weight, structural characteristics and solubility from these proteins.